Dynamic scan is one of the scan schemes used by X-ray computed tomography apparatuses. Dynamic scan is a scheme of repeatedly scanning a scan region at the same position while the top position is fixed. Dynamic scan allows to observe temporal changes in the same scan region. For example, dynamic scan is often used to observe movements and blood flow dynamics in a subject.
When acquiring image data corresponding to at least one respiratory cycle by a dynamic scan, the operator needs to determine by himself/herself an X-ray irradiation start timing and an X-ray irradiation stop timing. Subjects differ in respiratory motion. Even the same subject undergoes changes in respiratory motion in different situations at different times. An attempt to accurately execute a dynamic scan corresponding to only one respiratory cycle may quicken the irradiation stop timing to result in insufficient scan time. In addition, an attempt to avoid a lack of scan time may quicken the irradiation start timing. As a consequence, the scan time may exceed one respiratory cycle. As described above, it is difficult to accurately execute a dynamic scan corresponding to one respiratory cycle.